Urea-formaldehyde molding composition



Patented Nov. 30, 1943 rmEA-roammnmn MOLDING comosrrron Franz Nozicka, Vienna, Germany: vested in the Alien Property Custodian No Drawing. Application December 5, 1939, Serial No. 307,706. In Germany October 28, 19:8

\ 6 Claims. "('01. 260-71) This invention relates to a method for the production of press masses, and in particular of storage-proof quick or rapid press masses from urea and formaldehyde, and an acid dissociating hard- 1 ening medium.

When producing press masses from urea-formaldehyde-resins, which masses have to satisfy all modern requirements, such as quick press masses, it is necessary that, for'obtaining very high water stability (boiling-proof) and rapid hardening speed, in addition to a proper condensation procedure and the correct urea-formaldehyde proportion, suflicient acid be available in the press. Further, it is necessary that the mass for pressing have at a temperature of 35 to 40 such storing stability that the flowing capability and the other pressing properties are not altered after storing for several months. A press mass corresponding to all requirements must further have the property that, durin the pressing operation, the acid becomes effective only gradually so that during the flowing proceeding no hardening of the material takes place, as otherwise, especially when pressing large-size articles, obstructions will occur which prevent perfect pressing. The acid must, however, also not begin to act too late, as otherwise the hardening period is lengthened too much,

To satisfy all these requirements the acid in the press powder must be present in such form, that at temperatures from 35 to 40 no acid is split off, even after storing for months, and that the press powder has an approximately neutral reaction. During the pressing operation the acid must be liberated only at a temperature which is near 100, in order that just sufficient time remains for the uniform outflow andthat no ob struction occurs.

In the prior art the ammonium salts of weak and strong acids, the salts of hexamethylenetetramine, of organic bases such as aniline, methylamine, dimethylamine and trimethylamine or ethylamirie, diethylamine, and triethylamine, ethanolamine and others have been mentioned as substances giving off acid or developing acid. All these compounds have, however, the inconvenience that the salts either undergo strongly hydrolytic dissociation and therefore impart to the press powder a more or less strong acid reaction, or, as all urea-formaldehyde press ma'sses contain small quantities of free formaldehyde or split them off during the storing, opportunity is given that the acid is gradually liberated by the formaldehyde of various kinds.

obviate these inconveniences by addition of acid anhydrides, such as anhydride of benzoic acid or anhydride of malonic acid and so forth, or esters All these compounds, however, become saponifled in the course of time by the small quantities of water contained in any press powder and slowly cause acidification of the press masses. Other disclosures attempt to solve the problem by employment of compounds such as, for instance, fl-hydrobromic cinnamic acid or anhydrides of isodibromic succinic acid.

These compounds, however, give off acid only slowly during the pressing operation or they do not attain the necessary pH.

4 It has been found that a group of compounds possesses all the above mentioned required properties, which group is produced if hexamethylenetetramine is treated with formaldehyde, i. e., 1

mol hexamethylenetetramine with at least 2 mol formaldehyde. In this manner a combination of these two compounds takes place, which is up to the present not yet explained and which represents a quite considerably .stronger base than hexamethylenetetramine and the salts of which are only very weakly hydrolytically dissociated. one mol of this compound in normal solution with mol HCl shows a pH of 6.2. A hexa solution of the same strength, to which /2 mol HCl is added, shows a pH of about 2.

The fatty acid salts of these novel hexamethylenetetramine-f0rmaldehyde compounds form transparent gels, which are easily soluble in aqueous urea-formaldehyde solutions. For hardening urea-formaldehyde resins gel-like mixed salts of fatty acids and of another acid such as chloracetic acid, lactic acid or mineral acid have proved particularly suitable.

As the formaldehyde is apparently bound only loosely, these salts are always very resistant when care has been taken that no formaldehyde is consumed by any reactions. Only at temperatures near the compound is rapidly dissociated and opportunity is thus given that the whole acid can fully act. Normal urea-formaldehyde condensates have always the tendency to split off small quantities of formaldehyde, and in these the said compounds are therefore very stable. By variation of the mol-proportion of hexamethylnetetramine to formaldehyde, it is possible to alter the dissociation temperature of the compound. At about 1 mol hexamethylene-v tetramine for 3 mol formaldehyde the highest value is attained. Experiments to isolate the hexamethylenetetramine formaldehyde compound (especially fatty acid salts) make it possible to assume that 5 mol hexamethylenetetramine with 12 mol formaldehyde react to form a monoacid base.

For special purposethe easily isolatable, mostly .well crystallising double salts of the hexamethylenetetramine-formaldehyde compound, with an .acid and heavy metal salts or alkali salts or ammonium salts stood the test. crystallised double compounds of hexamethylenetetramine-formaldehyde-acids and heavy metal salts have been described by Marcel Delepine C. r. de lAcadmie des Sciences 127.622-25.

As suitable condensation methods of urea and formaldehyde or of urea-thio-urea and formaldehyde, all those methods have shown to be suitable, in which the smallest quantity of formaldehyde is employed, which results in a condensation product which no longer takes up further quantities of formaldehyde.

Example 1.-As a starting material there is used a product which is obtained by condensing urea and formaldehyde in a mol-proportion of 1:13 to 1:15 at neutral reaction and temperatures of 30 to 40 for 48 hours. To a proportion of the condensate containing 360 g. urea which is obtained, the gel-like compound of 12 g. hexamethylenetetramine, 8 g. lauric acid, 0.5 g. chloracetic acid and 6 g. formaldehyde are added. Filling substances, such as for instance cellulose, are then worked into the mass which has been obtained, and the mixture is then treated in the usual manner, for instance shaped while heating by pressure. Instead of formaldehyde other aldehydes, aliphatic as well as aromatic, for instance benzaldehyde, can be reacted ,with hexamethylenetetramine and acids.

Example 2.To a urea-formaldehyde condensation product which contains 360 g. urea the gel-like mixture of 10 g. hexamethylenetetramine and 6 g. of palmitic acid, 2 g. cetylic alcohol, 0.5 g. maleic acid and 20 g. cinnamic aldehyde are added as hardening medium, and the mixture thus obtained, which reacts approximately neutral, is kneaded with cellulose and treated in the usual manner to produce press powder. Instead of cinnamic aldehyde the equivalent quantity of benzaldehyde may be used.

The use of toluene-disulfamide resins has also proved to be advantageous, by which addition the flow and the water resisting property are further improved.

Instead of employing prepared hexamethylenetetramine the process can be carried out in such a manner that by addition of ammonia to the condensate the hexamethylenetetramine is formed in the condensate itself. These types of compounds may be employed with great advantage also for the production of castings from ureaformaldehyde resins, as by keeping correctly increased drying temperatures it is possible to carry through the dehydration of the cast articles without hardening and to make the final acid hardening take place only at increased temperature.

Also hot varnishes of urea-formaldehyde resins give excellently brilliant elastic films when these compounds are used as the hardening medium.

I claim:

1. A storage-proof quick press'mass comprising a condensation product or urea and formaldehyd and a hardening agent capable of dissociating to give acid reaction under molding conditions, said hardening agent comprising a carboxylic acid salt of a reaction product of 1 mol of hexamethylenetetramine with at least two mols of an aldehyde, said salt retaining a substantially neutral reaction at ordinary temperaure.

2. A storage-proof quick press mass comprising a condensation product of urea and formaldehyde and a hardening agent capable of dissociating to give acid reaction under molding conditions, said hardening agent comprising a carboxylic acid salt of a reaction product of 1 mol of hexamethylenetetramine with at least two mols of formaldehyde, said salt retaining a substantially neutral reaction at ordinary temperature.

3. A storage-proof quick press mass comprising a condensation product of urea and formaldehyde and a hardening agent capable of dissociating to give acid reaction under molding conditions, said hardening agent comprising a fatty acid salt of a reaction product of 1 mol of hexamethylenetetramine with at least two mols of formaldehyde, said salt retaining a substantially neutral reaction at ordinary temperature.

4. A storage-proof quick press mass comprising a condensation product of urea and formaldehyde and a hardening agent capable of dissociating to give acid reaction under molding condi tions, said hardening agent comprising a mixed salt formed by a carboxylic acid and another acid and by a reaction product of 1 mol of hexamethylenetetramine with at least two mols of formaldehyde, said salt retaining a substantially neutral reaction at ordinary temperature.

5. A storage-proof quick press mass comprising a condensation product of urea and formaldehyde and a hardening agent capable of dissociating to give acid reaction under molding conditions, said hardening agent comprising a mixed salt formed by a fatty acid and a mineral acid and by a reaction product of 1 mol of hexamethylenetetramine with at least two mols of formaldehyde, said salt retaining a. substantially neutral reaction at ordinary temperature.

6. A storage-proof quick press mass comprising a condensation product of urea and formaldehyde, said product being substantially incapable of taking up an additional quantity of formaldehyde and a hardening agent comprising a carboxylic acid salt of a reaction product of 1 mol of hexamethylenetetramine with 2 to 3 mols of formaldehyde, said salt retaining a substantially neutral reaction at ordinary temperatures.

FRANZ NOZICKA. 

